Improved residual oil conversion process for the production of chemicals



IMPROVED RESIDUAL OIL CONVER SION PROCES Oct. 23, 1956 c. N. KIMBERLIN,JR ET AL 5 2,768,127

FOR THE PRODUCTION OF CHEMICALS Filed May 17, 1951 2 Sheets-SheetZ J f T0 m m T J L9 2 Q) L9 L10 8 T +5 2: W I

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- CELczrlL EL. dclanzs 45g NW (lbborrzeg U itr d es Paten IMPROVEDRESIDUAL on. CONVERSION" PROC- ESS FOR THE PRODUCTION OF CHEMICALSCharles N. Kimberlin, Jr., and Clark E. Adams, Baton Rouge, La.,assignors to Esso Research and Engineering Company, a corporation ofDelaware Application May 17, 1951, Serial No. 226,892

1 Claim; (Cl. 196-55) The present invention relates to the production ofvaluable chemical materials from hydrocarbonaceous mate- Moreparticularly, the invention pertains to the aromatc and unsaturatedcompounds which are useful as chemicals or starting materials therefor.In brief compass, the invention provides for contacting heavy residuesof the type specified with subdivided solids at conditions conducive tothe formation of lower boiling highly aromatic or unsaturatedhydrocarbons and coke, in the absence of added steam.

In conventional petroleum refining the crude oil is first distilled toproduce various distillate fractions and a residue boiling above about700 F. or, with the more modern vacuum distillation equipment, theresidue may boil above about 1050 F. Motor fuels being the most valuableproduct of commercial refining, the value of the various fractions ofthe crude distillation is determined chiefly by their utility for theproduction of high quality motor fuels. Aside from virgin naphthas, thegas oil fractions are the most valuable from this point of view, becausethey may be readily converted by thermal or catalytic cracking into highquality gasoline. The distillation residue is the least valuablepetroleum product since it yields excessive amounts of coke and onlyrelatively small proportions of volatile products useful for theproduction of motor fuels.

It has been found that distillate oils such ,as naphthas and gas oilsare converted into more aromatic and unsaturated products useful forchemicals production when these oils are subjected to thermal crackingin fired coils at high temperatures of about 1000-1400 F., particularlyin the presence of steam. However, as pointed out above, the value ofthese oils as starting materials for motor fuels is normally too high tomake their utilization for the production of chemicals desirable undernormal circumstances. The situation with respect to distillationresidues is reversed. They are plentiful and inexpensive enough to serveas starting materials for chemicals on a theoretically economical basis.However, experiments have shown that high temperature thermal steamcracking in a manner similar to that used for the aromatization ofdistillate oils is inoperative on the basis of residual oils as the feedstock. Excessive coke formation and deposition in the cracking coilsleading to overheating and equipment plugging preclude operation on acommercial scale. In addition, it has been found that the steam reactswith the coke at the prevailing high temperatures to form substantialamounts of CO which dilutes the product vapors and seriously complicatesproduct recovery. When the steam supply is reduced or omitted cokeformation is further increased to become entirely prohibitive even fromthe point of view of product distribution. The present inventionovercomes these difficulties.

It is, therefore, the principal object of the present invention toprovide an improved process of producing highly aromatic and unsaturatedvolatile materials by cracking heavy hydrocarbonaceous residues. Otherand more specific objects and advantages will appear from the followingdescription of the invention wherein reference will be made to theaccompanying drawing in which Figure l is a semi diagrammaticalillustration of a system suitable to carry out the process of theinvention; and

Figure 2 is a similar illustration of a preferred application of theprocess illustrated by Figure 1.

It has now been found that heavy residues of the type specified may beconverted into lower boiling products rich in unsaturated and aromaticcompounds in commercially feasible operation by contacting the feed withsubdivided solids at coking conditions comprising high temperatures inthe range of about 12001400 F., preferably in excess of about 1250 F.,in the absence of added steam. The contacting of the oil with the solidsis accomplished by use of a transfer line reactor and/or a fluid bedreactor, the latter being the preferred embodiment of this invention.

In carrying out this preferred embodiment, the liquid or partiallyvaporized reduced crude or similar heavy residue is injected into arelatively dense turbulent bed of subdivided contact solids having aparticle size of about 30-400 mesh, fluidized by a gaseous mediumflowing upwardly through the bed at a linear superficial velocity ofabout 0.3-5 ft. per second to give the bed the appearance of a boilingliquid separated by a definite interface from an upper dilute suspensionof solids in gasiform products. Hydrocarbon gases, such as propane orother light hydrocarbons such as butanes, ethane or mixtures thereof areused in place of steam as the auxiliary fluidizing medium required tomaintain the solids bed in the fluidized state. The amount of thesehydrocarbon gases used as auxiliary fluidizing agents will ordinarily bein the range of 1-10 wt. percent of the residuum feed. However, thesegases themselves are converted into valuable chemicals and under somecircumstances it may be economically attractive to use much higherproportions of these gases; in such cases the amount of lighthydrocarbon gases fed may be 23 times the amount of the residuum feed.

The temperature of the fluidized bed is maintained at about l2501400 F.conducive to the deposition of coke on the fluidized solids and to theformation of highly aromatic and olefinic volatile products which arewithdrawn overhead to be worked up into chemicals by fractionaldistillation, solvent extraction, selective adsorption, azeotropic andextractive distillation, and other methods.

The heat required to maintain the fluidized bed at the desiredtemperature may be supplied by indirect heating. However, in accordancewith the preferred method of heat supply coke-carrying solids arecontinuously passed from the coking zone to a combustion zone whereincoke is burnt oif to heat the solids to a temperature higher than cokingtemperature. Hot solids are continuously recirculated to the coking zonein amounts suflicient to supply the required heat therein. The carriersolids may be either inert or catalytically active, such as coke, sand,silica gel, various natural or activated clays, used cracking catalysts,etc. However, coke produced in the coking stage is the preferred carriersolid in normal operation.

When operating in the manner described, coke deposition on the reactorwalls is prevented by the scouring effect of the highly turbulent solidsand by the fact that coke is preferentially deposited on the finelydivided solids which have a large surface area. In addition, theexposure of the feed to this large surface area increases overallconversion and the yield of valuable volatile products. The hightemperatures employed are conducive to the formation of aromatics andolefins in large proport atenred oer-.23, s

ored at the coking and product recovery conditions of the process.

Having set forth its objects and general nature, the in vention .will bebest understood from the following more detailed description I of thesystem illustrated by the drawing.

Referring now to Figure 1 of the drawing, a heavy residual oil such asvacuum still bottoms from the distillation of a South Louisiana crude,said bottoms having anAPI gravity of about 12- and a Conradson carboncontent of about 17% which may be, preheated to about 500-700 F.- issupplied through: line-1 to a lower portion of coker 3. Line 1 maydischarge, into reactor 3 at apoint above a suitable gas distributingmeans, such as a perforated plate or grid 5, through a spray nozzle 7 ofconventional design adapted to eject the predominantly liquid feed inthe form of a fine mist or spray. Coker 3 contains a mass M3 ofsubdivided solids, preferably coke, having an average particle size ofabout 50200 mesh. Mass Ma is maintained in reactor 3 at aboutatmospheric or any desired higher pressure in the form of a dense highlyturbulent fluidized solids bed having an upper interface L3, with theaid of hydrocarbon gases, preferably rich in propane, introduced throughline 9 and grid in amounts sufiicient to establish a linear superficialgas velocity within mass Ma of about 0.3-1.5 ft. per second. Mass N13 ismaintained at a temperature of about 12501400 F., preferably above 1300F., conducive to coking and the formation of highly aromatic andolefinic volatile coking products as will appear hereinafter.

The vaporous coking products are carried by the fluidizing gas overheadfrom level L3 and may be withdrawn from coker 3 via suitable gas solidsseparation means, such as cyclone separator 13 provided with solidsreturn pipe 15. Product vapors now substantially free of entrainedsolids are passed via line 17 to product separation and recoveryequipment schematically indicated at 18 to be worked up therein ashereinafter described. The hot products leaving reactor 3 by line 17preferably have theirtemperature reduced to the range of 850-1100 F. bymeans of a quench fluid introduced from line 19 into line 17. Thisquench oil may be water but is preferably a recycle fraction ofintermediate boiling range of about 400700 F.

Returning now to mass M3, coke-carrying solids are withdrawn downwardlythrough a conventional standpipe 21 aerated and/ or stripped by one ormore taps t. Product coke amounting to about -22% of the residuum whenfeeding the South Louisiana residuum specified may be recovered throughbranch standpipe 23. The remaining solids are supplied to line 25wherein they are picked up by air and carried in suspension to a bottomportion of burner 27 preferably through a suitable distributing device,such as grid 29. Flow conditions are so controlled that a dense,turbulent, fluidized mass M27 is formed above grid 29, similar to massMa. Combustion takes place in mass M27 as a result of which the solidsare heated to about 1300-l600 F., preferably about 50200 F. higher thanthe temperature of mass M3. Flue gases are withdrawn overhead via line31 preferably after. fines separation and return by cyclone 33 anddippipe 35. Reheated solids are withdrawn downwardly from mass M27through standpipe 37 aerated and/or stripped through taps t. The hotsolids may discharge from standpipe 37 directly into mass M3 at a ratesutficient to supply as sensible heat of solids the heat required in,coker 3. It maybe desirable to re-adjust the particle size of thecirculating solids continuously orat intervals to prevent accumulationof particles of excessive size.

This may be accomplished by subjecting the solids withdrawn through.standpipeZl to grinding in. any. suitable...

conventional manner. A supersonic attriter may be arranged in anyportion of the solids circulation system in a manner known per se in theart of catalytic cracking.

The system illustrated in Figure 1 permits of various modifications. Forexample, the feed may be supplied together. with. the fluidizing gasthroughgrid 7 without.

the use of a spray nozzle. In thiscase, it may be desirable to feed thereheated solids'from line 37 into the residuum feed line further topreheat, and vaporize the.

feed. In another. modification, the reheated solids may be mixed withtheresiduum feed via lines 38 and 40 and passed into a cyclone 42whence. cracked vapors discharge into line 17' and solids containingunvaporized feed discharge into mass. Ma This modification allows for avery short contact time for the bulk of the feed with the hot solids andthus favors liquid yield over gaseous yield. Other modifications willappear to those skilled in the art without deviating from the spirit ofthe invention;

When operating in the manner described above, the.

products recovered throughline 17 may amount to about wt. percent of thelight hydrocarbon gases fed plus about 75-82 wt. percent of the residuumfed. The products from the-light hydrocarbons comprise hydrogen andmethane and olefinic and diolefinic gases in the range of C2. to C4. Theproducts obtained from the residuum feed (South Louisiana residuum, forexample) are as,

follows:

(1). 30to 50 wt. percent .(based on residuum feed) of hydrogen and C1 toC3 hydrocarbons. The C2 hydrocarbons comprise 65-80% ethylene and 2035%ethane.

The Ca hydrocarbons comprise 80-95% propylene and.

5,20% ethane.

(2) 5 to .15 vol. percent C4 hydrocarbons comprising. about 15' to 30%butadiene, l to 5% butanes, and the.

remainder butenes.

(3) 2 m6 vol. percent Cs hydrocarbons comprising 30-50% diolefins(isoprene, piperylene, and cyclopentadiene) and the remainder pentenes.

(4) 8 to 20 vol. percent gasoline range hydrocarbons boiling about -400"F. and comprising about 50 80% aromatics; these aromatics are about flbenzene, toluene, and the remainder xylenes and C9 to C11 aromatics.

(5) 2 to 10-volume percent of intermediate fractionboiling at about400700 F. having an- API gravity of about 4l2.

(6) 2 to 10 vol. percent of tar boiling above 700 F. and having an APIgravity of about 20 -5.

One of the standard procedures used for upgrading crude residua incommercial refining practice is a thermal viscosity breaking orvisbreaking operation involving:

fuel oil, which is highly undesirable for economical reasons, since thetar amounts even in operations of highest cracking severity to at least50 wt. percent on feed. There is practically no outlet for the tarexcept as a residual fuel which is a low value product; furthermore inorder for the tar to be suitable even as a residual fuel it is necessaryto blend with it a part of the gas oil product in order to reduce theviscosity of the tar. Thus there are 3 highly desirable improvements ofthis process, viz., (l) to increase visbreaking severity in order toincrease the yield of naphtha and particularly of gas oil (which maybeultimately converted into high quality gasoline by catalytic cracking)and to decrease the yield of tar, (2) to avoid the blending of the gasoil fractions in the tar for use as residual fuel, and (3) to convertthe tar itself into products more valuable than residual fuel. Thepresent invention may be combined with conventional high severityvisbreaking to provide a process so improved. A combination process ofthis type is schematically illustrated in Figure 2.

Referring now to Figure 2, the system shown therein comprises aconventional visbreaking stage 52, a visbreaker product fractionator 58,and a coker 3 of the type of coker 3 of Figure 1. The functions andcooperation of these elements will now be described using the conversionof crude still bottoms as an example. Other feeds may be treated in asubstantially analogous manner.

In operation, a crude still residuum such as an atmospheric or vacuumdistillation residue boiling above about 800 F., preferably above 1050F., may be supplied from line 50 to visbreaking stage 52 at a preheatingtemperature of about 500750 F. and at a pressure of about 100-1500 p. s.i. g. suitable for high severity visbreaking. visbreaking stage 52 maycomprise one or more conventional furnace coils operated in parallel anddischarging into a soaking drum. The oil feed is cracked in the coilsand soaking drum at an elevated pressure preferably not lower than about500 p. s. i. g., a temperature of about 8501000 F. and a residence timeat visbreaking temperatures of about 1-30 minutes, corresponding to anoil throughput of about 75-2 volumes of liquid oil per volume ofvisbreaker space per hour (v./v./hr.). Up to this point the operation isconventional but preferably carried out at very high severity limited bythe operability, i. e. coking, of the equipment.

7 Now, rather than separating the visbroken eflluent into total liquidsand total vapors under pressure as it is common practice, the efiluentis directly flashed through line 54 provided with pressure release valve56 into a fractionator 58 which is preferably operated at atmosphericpressure. Slightly elevated pressures of, say, up to about 100 p. s. i.g. may be used. Stripping steam is admitted through line 60 to thebottom of fractionator 58. Distillation in fractionator 58 is soconducted that an overhead fraction of gas and naphtha boiling up toabout 350-400 F. is removed through line 62, gas oil is recoveredthrough line 64 and heavy bottoms boiling above about 800 F. arewithdrawn through line 66. This bottom fraction serves as feed to acoking system of the type illustrated in Figure 1 and shown in Figure 2at 3 in a simplified manner using like reference characters to identifylike system elements.

A portion of the overhead fraction leaving fractionator 58 through line62 is branched off through line 68 and supplied to line 9 to serve asthe auxiliary fluidizing medium for mass M3 substantially as describedwith reference to Figure 1. The fractionator bottoms in line 66,representing the oil feed to coker 3 are fed together with thefluidizing medium via line 9 and grid 5. Solids circulation and heatsupply take place through standpipes 21 and 37 as described withreference to Figure 1. Volatile products withdrawal and recovery arelikewise substantially identical with those described above. The gas oilfraction Withdrawn by line 64 may be used for any desired purpose, butis preferably converted into high quality motor fuels by catalyticcracking.

Regarding product distribution, the products from the visbreaker tar areessentially the same as those from the virgin residuum feeds describedwith reference to Figure 1 except that the yield of coke is higher andthe yields of gaseous and liquid products are proportionally less. Theyield of coke from the visbreaker tar will depend upon the severity ofthe visbreaking operation and may vary from 20% higher to 100% higherthan the coke yield from the virgin residuum from which the tar wasderived.

In general, the products will vary with the relative proportions ofresiduum or tar and lighter hydrocarbons feed to the coker. The residualfeed tends to give more bydrogen-deficient products, i. e., higherconcentrations of aromatics and somewhat higher concentrations ofolefins and diolefins in the non-aromatic products.

The system of Figure 2 may be modified in several respects. For example,if desired the entire overhead fraction, gas and naphtha leavingfractionator 58 by line 62 may be diverted by line 68 into line 69,since the naphtha from the visbreaking operation is of relatively lowoctane number and ordinarily requires further processing, such asreforming, before use as a motor fuel. When so diverted the naphthafraction is converted into (1) about 3555 wt. percent of gasescomprising hydrogen plus C1 to C3 hydrocarbons, the C and C3 beinghighly olefinic, (2) 5-l5 vol. percent C4 and C5 comprising olefins anddiolefins, (3) 2045 vol. percent gasoline range hydrocarbons boiling inthe range of about 400 F. and comprising 30-55% of aromatics, and (4)about 5-10 vol. percent of heavier product boiling above about 400 F.Other modifications within the spirit of the invention may appear tothose skilled in the art.

The above description and exemplary operations have served to illustratespecific embodiments of the invention but are not intended to belimiting in scope.

What is claimed is:

A fluidized solids coking process of producing volatile products rich inaromatic and olefinic constituents from heavy hydrocarbonaceousresidues, which comprises passing said residues in contact with asubstantial mass of substantially non-catalytic subdivided solids heatedto a temperature of about 13001600 F. and a normally gasiformhydrocarbon conveying gas through a narrowly confined extended path at aconversion temperature of about 1250-1400 F. in the absence of steam andfor a relatively short time adapted to convert a portion of saidresidues into said volatile products while leaving another portion ofsaid residues substantially unconverted, said unconverted portion beingdeposited on said solids, separating said solids from the volatileproducts formed, passing said separated solids carrying said depositedportion substantially at said conversion temperature to a coking zone,maintaining said solids in said coking zone in the form of a dense,turbulent, fluidized mass for a relatively long time sufficient tocomplete conversion of said deposited portion into coke and volatileproducts, introducing normally gasiform hydrocarbons into said cokingzone to promote fluidization and to convert at least a portion of saidgasiform hydrocarbons, withdrawing volatile coking products overheadfrom said coking zone, separately withdrawing coked solids from saidcoking zone, reheating said withdrawn solids to said first-namedtemperature and supplying solids so reheated to said path.

References Cited in the file of this patent UNITED STATES PATENTS1,419,123 Rittman June 6, 1922 2,114,416 Donnelly Apr. 19, 19382,133,344 Cooke Oct. 18, 1938 2,326,186 Watson Aug. 10, 1943 2,340,974Myers Feb. 8, 1944 2,445,328 Keith July 20, 1948 2,527,575 Roetheli Oct.31, 1950 2,543,884 Weikart Mar. 6, 1951 2,636,844 Kimberlin, Jr. et a1Apr. 28, 1953 2,661,324 Letter Dec. 1, 1953 OTHER REFERENCES Sachanen;Conversion of Petroleum, 2d edition 1948 pp. 252-254.

